This invention relates to an intelligent additive manufacturing approach, and more particularly an approach that makes use of one or more of machine learning, feedback using machine vision, and determination of machine state.
Additive manufacturing (AM) is a set of methods that allows objects to be fabricated via selective addition of material. A typical additive manufacturing process works by slicing a digital model (for example, represented using an STL file) into a series of layers. Then the layers are sent to a fabrication apparatus that deposits the layers one by one from the bottom to the top. Additive manufacturing is rapidly gaining popularity in a variety of markets including automotive, aerospace, medical devices, pharmaceuticals, and industrial tooling.
The growth of additive manufacturing processes has led to various iterations of such processes being commercialized, including extrusion processes, such as Fused Deposition Modeling® (FDM®), light polymerization processes, such as stereolithography (SLA) and multijet/polyjet, powder bed fusion processes, such as selective laser sintering (SLS) or binder jetting, and lamination processes, such as laminated object manufacturing (LOM). Nevertheless, despite this growth and rapid progress, additive manufacturing has limitations, such as the materials that can be used in conjunction with such processes. There are limited types of materials, and the performance of the materials limits the efficiency and quality that results.
Inkjet 3D printing is a method of additive manufacturing where printheads deposit droplets of liquid ink. Printheads are typically mounted on a gantry system to allow deposition of ink in different locations within the build volume. The build platform may also move with respect to the printheads, which may be stationary. The liquid ink is solidified using UV or visible-light radiation.
Multiple printheads may be used in one system in order to build objects with multiple base materials. For example, materials that have different optical, mechanical, thermal, electromagnetic properties can be used. These materials can be combined to achieve composite materials with a wide range of material properties.
The UV curing unit is typically one of the subsystems used within an inkjet additive manufacturing apparatus. UV radiation provides the means of solidifying inks via photo-initiation of the polymerization reaction. UV radiation can be supplied by a variety of different mechanisms such as arrays of LEDs and Mercury or Xenon arc lamps. UV curing is typically applied after each layer is printed or after each material within a layer is deposited. The UV curing unit can be fixed with respect to the printer or it can move independently with respect to the object.
Alternatively, ink solidification can be achieved by changes in thermal conditions. For example, a liquid material solidifies as its temperature is lowered. A variety of different inks can be used in this category such as waxes. Both UV-phase change inks and thermal-phase change inks can be combined to manufacture an object.
Because of the slight variation of each drop and surface tension of inks, liquid layers deposited onto the platform are not perfectly flat, requiring a mechanical flattening device in order to eliminate the error and error accumulation caused by uneven layers. The flattening device may be a roller, script, or even mill, etc. Typically, about 20-30% of jetted material is removed during the flattening process, resulting in significant waste and increased material cost.
3D printed objects when manufactured using an inkjet process may need structural support. For example, most objects with overhangs need support structures. Typically, additional print data is generated for these support structures. In inkjet additive manufacturing, typically a separate ink is designated as a support material. This ink is deposited also using printheads and then it is solidified. It is desirable for the support material to be easily removed after the print is completed. There are many potential support materials including UV-curable materials that are soluble in water or other solvents or wax-based materials that can be removed by melting.
After the printing process is completed, parts are typically post-processed. For example, support material may need to be removed. The parts might also need to be post-processed to improve their mechanical or thermal properties. This may include thermal treatment and/or additional UV exposure.
Inks suitable for inkjet printing need to conform to certain specifications. The key requirements include: 1) viscosity typically needs to be within 3-15 cps at the operating conditions; 2) surface tension typically should be between 20-45 mN/m; 3) thermal stability—the ink should not solidify within the printhead, ink container, or feeding system; 4) formulation stability—different components of the ink should not separate for a reasonably long time. Inks are typically optimized in order to meet the specifications for printing.
Furthermore, the waveform for driving the printheads must be optimized and adapted for each ink. Moreover, many different parameters of the printing process need to be adapted for individual inks, such as printhead and ink pre-heating
In many cases inks may include additives. These additives include colorants in the form of dyes or pigments or the mixture of pigments and dyes that are dispersed or dissolved in the ink. Surfactants may also be used to adjust the surface tension of the ink for improved jetting or printing performance. In addition, other types of particles or additives may be used in order to enhance the mechanical, thermal or optical characteristics of the cured resin.